The present invention relates, in general, to cable communication systems, and more particularly to cable data communication systems.
Cable communication systems are being designed to handle a wide variety of services including telephony, video and data. One method of integrating these services is by using a system similar to cable television systems. The cable network consists of several cables, splitters, combiners and amplifiers. A plurality of customer premise devices such as televisions, computers, set top boxes and modems are typically connected to a cable network through a single coaxial cable routed throughout the customer premise. The connection is made to the cable network through a cable access unit which is typically mounted on the outside of the customer premise. Other customer premise equipment such as telephones and FAX machines may be connected to the cable access unit through other types of cabling such as twisted pair wiring.
Typically, a frequency band is chosen for upstream transmissions (transmissions from the customer premise to the network) which is different from the frequency band for downstream transmissions (transmissions from the network into the customer premise).
Poor connections, faulty cables, and noise from customer premise devices introduced in the upstream frequency band contribute to ingress noise in the cable network. Faulty connections and broken cables couple radio signals and noise into the cable network. In addition, customer premise devices may introduce noise generated in the customer premise device into the cable network. Local oscillators and phase lock loops, for example, may generate harmonics in the upstream frequency band and be a source of ingress noise.
Since the customer is responsible for the cabling inside the customer premise, the service provider typically cannot control or predict the quality and condition of the cabling and customer premise devices in the customer premise. Noise in the upstream frequency band cannot be eliminated by simple filtering since the frequency at which the noise occurs cannot be predicted and since the noise will likely occur in a channel that is being used for upstream communication and, therefore, cannot not be attenuated. Ingress noise becomes more problematic as the number of customers on the cable network increases.
Typical cable communication systems power the subscriber cable access units from the network through the cable. This allows for the system to operate when power is not available through the subscriber premise. Although the power consumption of each individual cable access unit may not be large, the combined power requirements on the network are significant. A slight reduction of power consumption of each cable access unit can greatly reduce the demand on the system.
Therefore, there exists a need for a method and device for reducing the level of ingress noise and reducing power consumption in a cable communication system.